1. Field of the Invention
This invention relates to friction reduction for turbulent high pressure water streams for use, for example, in firefighting applications. In one of its aspects, the invention relates to a novel composition which can be added to a turbulent stream of water at the point of use. In another of its aspects, the invention relates to a method for reducing drag in high pressure water streams.
2. State of the Prior Art
The term "drag reduction," as it is known in the fluid flow art, is the increase in volumetric flow rate of a fluid at given pressure drop due to the addition (usually of a small amount, e.g., 200 ppm or less) of a solid, linear polymeric material of relatively high molecular weight. Such material is known as the "drag reducing agent." The term "hydrodynamic drag reducing efficiency" is a measure of the percent increase in the flow rate of treated water (which contains the hydrodynamic drag reducing agent) relative to the flow rate of untreated water (lacking the hydrodynamic drag reducing agent).
In the past few years considerable effort has been expended in attempts to devise methods for introducing drag-reducing polymers into aqueous streams. For example, concentrated aqueous solutions of the drag reducing agent can be injected into the water stream to be treated. The drag-reducing polymer has its highest "hydrodynamic drag reducing efficiency" at concentrations of from 50 ppm to 200 ppm. It is convenient to make up a concentrated solution containing the 1 percent or more of the drag reducing polymer and to inject this solution into the aqueous stream to be treated at a rate sufficient to yield the optimum concentration in the treated stream. However, this procedure has shortcomings. Poly(ethylene oxide) of molecular weight 4,000,000 is very efficient drag-reducing polymer but, because of its high molecular weight, concentrated solutions are extremely viscous. Dissolution is also very difficult. The poly(ethylene oxide) particles tend to stick together and form agglomerates during the dissolution process. Solutions higher in concentration than one percent are difficult to pump with conventional equipment. Furthermore, the viscous concentrate does not mix readily with the aqueous stream to be treated. Also aqueous solutions of poly(ethylene oxide) degrade on storage and their hydrodynamic drag reducing efficiency is lost.
Another approach is the use of slurries of drag reducing polymer in an organic solvent which is a non-solvent for the drag reducing polymer. For example, a slurry of a finely divided poly(ethylene oxide) can be prepared in a water-soluble carrier fluid such as propylene glycol. This slurry is injected into the aqueous stream to be treated. The particulate polymer particles dissolve in the water and impart the desired drag reducing effect. Slurries can contain 30 percent by weight or more of poly(ethylene oxide). Consequently, slurries require smaller storage containers for the amount of polymer required to treat a given volume of water than do aqueous stock solutions, where the maximum concentration which can be effectively utilized is one percent or less.
The slurry system of introducing poly(ethylene oxide) into aqueous streams has been developed for use in fire fighting applications. The slurry can be dispensed from a container holding about 20 gallons carried on the fire truck. It is injected by mechanical pumping into the water at the suction side of the water impeller pump.
In the various techniques discussed above, the methods employed for introducing the drag reducing agents into the aqueous streams generally utilize an apparatus which was adapted to store and "inject" proportionate amounts of the vehicle containing the drag reducing agent into the flowing aqueous stream. The conventional apparatus is complex in nature and usually includes the necessary valves, pumps, storage containers, electrical systems and injection devices which create problems due to the tendency of the drag reducing agent to agglomerate in the system. Moreover, breakdowns occur due to normal mechanical failure in the system. Further, the cost of the slurry and the equipment is high.
Another method of introducing poly(ethylene oxide) into an aqueous stream utilizes a tablet consisting of a physical mixture of poly(ethylene oxide) and a water-soluble organic or inorganic material, both ingredients being in finely divided powdered form. The mixture is compressed into the tablets, preferably in the form of cylinders about one-half inch high and about one-half inch in diameter. Tablets of this type are placed in a canister and the canister, in turn, is inserted into the stream to be treated. Water flowing through the interstitial spaces between tablets causes them to dissolve. With the tablet form, however, it has been difficult to achieve the optimum concentration of the polymer in a high pressure water stream. Further, the results are irregular and blockage takes place in the delivery systems. It is quite difficult to accurately meter the desired concentrations into the water systems.
Water soluble polymers other than poly(ethylene oxide) are also effective drag reducing agents when dissolved at low concentrations in aqueous streams. Polymers known to be effective are polyacrylamide, certain cellulose derivatives such as hydroxyethyl cellulose or methoxy cellulose, and certain polymers derived from natural products, e.g., guar gum or akra bean extract. In general the problems associated with practical use of these polymers are similar to those encountered with poly(ethylene oxide). In order to be an effective drag reducing agent, a polymer must be very high in molecular weight. Therefore aqueous stock solutions of concentrations high enough to be usable for injection into the aqueous stream to be treated are very viscous and difficult to pump.